How do I stop my Ferroli Modena 80 E gas boiler sparking once it is lit ?

The boiler recently stopped firing up on DHW and CH. When I moved the flame sensor electrode cable at the main board terminal the system started up and continued to run while held in place. 36 hours later the system failed again - no spark. I checked the air pressure switch which was ok but found poor cable terminal connections at the main board. These were repaired and sparking and ignition were restored though the sparking now continues when the burner is lit. The flame sensor electrode and wiring to the main board seem ok - current returned to main board from electrode when flames are present. Can this fault be cured other than by replacing the main board and, if not, are there any checks that need to be made to avoid damage to the new replacement? Any advice gratefully received. Thanks